Many proteins are synthesized as inactive zymogens which are converted to active proteins by "limited proteolysis" of peptide bonds. Zymogen activation serves as a control mechanism whereby physiological signals are rapidly and irreversibly amplified in a poised system. The aims of the present study are fourfold: 1) Identification of the changes in protein structure which correlate with appearance of biological activity during zymogen activation in digestion, blood coagulation, fertilization and related processes. 2) Identification of the mechanisms whereby the process of zymogen activation is induced and terminated. 3) Exploration of the role of limited proteolysis during protein synthesis and in the initiation of intracellular protein degradation. 4) Development and application of microchemical methods of amino acid sequence analysis in order to compare homologous proteins of diverse function, to establish the covalent structure necessary for relating three dimensional structure to function, and to explore limited proteolytic processes in physiologically important zymogens.